1. Field of the Invention
The present invention relates to a method of and an apparatus for generating an alarm in the event of access of a working vehicle to a worker working in the same working area as the vehicle. More particularly, the invention is concerned with a method of and an apparatus for detecting the position of a worker with respect to the working vehicle by making use of ultrasonic waves and for activating alarm, as necessary.
2. Related Art
Maintenance of an aircraft requires many large-size transporting vehicles for transporting various parts of the aircraft. These transporting vehicles travel in the area around the aircraft, which area contains many workers. Similarly, by road construction sites, construction machinery or vehicles, such as road rollers, work in areas where many workers work together. The operation of such vehicles involves a substantial danger that workers may accidentally be injured by contact with a vehicle, particularly when the vehicle is moving backwards. In order to eliminate such a danger, it has been a common measure to attach a device known as back sonar to a suitable portion of a vehicle. The back sonar serves as a safety device which, upon detection of an unidentified object which has accessed the vehicle, activates an alarm or automatically puts the brake of the vehicle into effect thereby stopping the vehicle.
Sensors such as back sonar, however, are disadvantageous in that they are sensitive to all the objects which reside in the area covered by the sensor, so that the vehicle may undesirably be stopped in response to detection of an object such as an electric pole or a fence, causing a serious impediment to the performance of the work.
In particular, in construction sites, workers are often obliged to work without taking into account the approach of working vehicles or without facing such vehicles at all for a long time. Thus, the workers often have to work without visually recognizing a vehicle, even when the vehicle is approaching. In fact, it often happens that a vehicle running backwards accidentally contacts a worker, who has not been aware of the access of the vehicle at all.
It is also to be pointed out that the sight of workers, particularly backward sight, is seriously impaired by helmets, which the workers are required to wear from the view point of safety.
This gives rise to the demand for a suitable measure for informing the worker of access of a working vehicle from the back side of the worker, thereby eliminating such danger.
The most practical and conventional method for avoiding such danger is to station a watcher who is in charge of watching the positions of workers in relation to moving vehicles. Obviously, however, the best method would be to enable each worker himself to be aware of access of any vehicle running therearound.